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      03-20-2012, 05:52 PM   #1
shiv@vishnu
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Drives: X1, 335i
Join Date: Sep 2006
Location: SF Bay, CA

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Exclamation Vishnu/FFTEC N54 Engine Development: Piston/Rod Comparison

Hi guys,
Sean@FFTEC and I spent a good bit of time mulling over the internals of the stock (11/07 production) N54 that we tore down last week. We've already learned quite a bit in the process. But we also have many more questions that we are looking to get answered. But that is for another time

In the meantime, we wanted to compare the N54 piston/rod assembly with something that we are VERY familiar with, the Mitsu Evo 4G63! Both Sean and I have spent years tuning stock (and built) 4G63s. Often running the same exact turbocharger we are using in my single turbo 335. So comparing the design of the two piston/rod assemblies makes sense. Next to getting the parts stress tested and properly analyzed (which is in the works), this is a good approach to getting an idea of what is (and isn't) possible with a completely stock N54 engine.

A stock 4G63, for instance, can reliably (i.e., long term) support 450lbft of torque before the rods buckle/bend. Which is ~115lbft/rod. All other things equal, if it had 6 cylinders, it should be able to support well over 600lb-ft of torque. Of course, not all other things are equal (stroke, piston speed, max revs, etc,.) Nonetheless, this is a decent starting point since we don't have any reasons to think that the n54 isn't stronger than the 4G63, stock for stock. If that is the case, the BMW will enjoy a 50% output advantage due to 50% larger displacement and 50% more pistons/rods. But still, it's a good idea to exercise restraint when running high midrange boost/torque pressures. Those looking to run 3.5bar map sensors just so they can run 22+psi of boost at peak torque might want to think twice

N54 (Left) vs 4g63 (Right)

It's nice to see that the N54 rod is considerably thicker and wider than the 4G63. The caps are also cracked which means that they are forged with the rest of the rod and literally cracked apart into 2 pieces. Advantages of this approach is improved strength/rigidity.


One thing we found interesting is how tapered the N54 rod is at the small end where it mates with the wrist pin. Maybe this is done to save weigh or reduce friction. But it would be our first point of concern when running higher rev limits or mis-shifting.
It's also interesting to see the bearing width on the big end of the rod (where it connects to crankshaft). It's considerably narrower than that of the 4G63. Which, all things equal, would mean less of a hydraulic "buffer" during detonation events. However, this narrow bearing design seems to be common among newer engines such as the Evo X's 4B11T engine which, as many know, can hold BIG power. So this narrow bearing doesn't necessary mean a weaker engine. It's also worth noting at the N54 crankshaft bearing surface (not shown) is beautifully polished and machined. It looks like an Evo crankshaft AFTER it has been sent out to be polished! There is no doubt that the tolerance level and general fit/finish on the BMW engine is in a class by itself.


Nice to see the N54 use a snap ring on both sides of the wrist pin. Not so with the 4G63.


Another angle showing the rod taper at the wrist pin.


The N54 piston has a slightly smaller skirt. Likely for reducing friction/rotational weight.


Like the 4G63, the N54 piston has nice fat ring lands. This is typical of a solid motor built for big boost. The 4G63 runs ~20psi boost from the factory, btw.

Over the next couple of weeks, we will be running some revealing tests on the stock pistons and rods. Tests that will give us a very clear indication of what kind of powers they can reliably support. We will run the same tests on the 4G63 piston/rods which will give us something to compare it to.

Very exciting times!

Cheers,
shiv

Some more pics/discussion on our Facebook page here: https://www.facebook.com/pages/Vishn...33431676670350

Last edited by shiv@vishnu; 03-20-2012 at 06:02 PM.
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